Single-crystal Films Of Copper Research Articles

Single-crystal copper films on sapphire

Single-crystal copper films on sapphire have recently been reported upon in relation to graphene growth on these films. In the present paper the kinetics of the formation of single crystal copper films is investigated. We demonstrate the importance of heating the sapphire substrate in 1000 hPa oxygen, followed by a fast cooling prior to depositing the copper film. The importance of this treatment is tentatively explained by the dissolution of oxygen in sapphire and subsequent out-diffusion during recrystallization of the copper film to form a copper-oxide interface layer. Also, the importance of avoiding oxygen incorporation in the sputter deposited film is demonstrated.

A Spontaneous Morphology Change on the Surface of Electrodeposited Single-Crystal Copper Films during Room-Temperature Aging

During room-temperature aging, a morphological transition described as a spontaneous morphology change was discovered to occur on the surface of single-crystal copper electrodeposits grown epitaxially on {001} copper substrates. Within half to two hours after the completion of deposition, well-defined periodic contour lines appeared suddenly around the originally smooth-faced pyramids. These contour lines were thought to represent periodic cracks/steps, which were formed to relieve tensile stress developed as a result of surface annihilations of excess vacancies trapped in the deposits. Thus the formation of these lines was phenomenologically the same as the sudden appearance of fine grains observed previously on the surface of polycrystalline copper electrodeposits during room-temperature aging.

A Spontaneous Morphology Change on the Surface of Electrodeposited Single-Crystal Copper Films during Room-Temperature Aging

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Energy distribution of metal and noble gas ions traversing single-crystal copper films

A comparative investigation of the energy distribution of ions that traversed single-crystal cooper films reveals that the energy loss of channeled and nonchanneled particles depends not only on the mass but also on the radius of bombarding ions. It is established that the energy spectra of transmitted ions are highly sensitive to a change in the composition and structure of the films. From the change in these spectra, one can estimate the degree of disordering in thin films under various applied forces.

A study of the orientation dependence of the electron energy loss spectra for single crystal films of copper and silver

Apart from two peaks caused by bulk and surface plasmons, four or five peaks (depending on the crystal type) of electron energy losses due to inter- and intraband electron transitions are observed in the investigation of the electron energy loss spectra for metals (Cu, Ag). A comparative analysis of the spectra for Cu or Ag films reveals a shift of bulk plasmon loss peaks to higher values for polycrystals, as in the case of transition metals and semiconductors. In a study concerning the orientation dependence of the energy loss spectra (ELS) for electrons scattered from the copper and silver surface, the anisotropy of the bulk plasmon peak is found when the incident beam’s polar angle or the sample’s azimuthal angle are altered. The anisotropy of the primary electron energy loss for plasmon excitation is also observed, depending on the sample orientation relative to the direction incident electrons. The energy losses are found to increase with an increasing atomic packing density of planes and crystal transparency relative to the incident beam.

Effects of Strain Rate on the Tensile Deformation of Single-Crystal Copper Films

Molecular dynamics (MD) simulations with an EAM potential are carried out to study the strain rate effects on the tensile deformation of single-crystal copper films. The stress, the atomic energy, as well as the atomic configurations of the systems are presented to explore the strain rate effects on copper films. It is found that yield stress increases with loading rate. Meanwhile, deformation mechanisms with different strain rates are analyzed in the present work. At lower strain rate, slips along {111} planes are primarily responsible for the plastic deformation in nano-Cu films. As strain rate increased, the motion of dislocations becomes easier, a transition of the deformation mechanism from sequential propagation of slips along well-defined slip planes to complex cross-slip.

Size effect in the low-field Hall coefficient of single-crystal copper films

Measurements of the low-field Hall coefficientRH of single-crystal copper films were made at 4.2 K by the use of a SQUID. The surface normaln of the samples was directed in the [100], [110], and [111] directions and the ratio of the thickness to the mean free path ranged from 0.1 to 0.7. It is found that the effect of surface scattering causesRH to decrease whenn ‖ [100], whereas it causesRH to increase whenn ‖ [110] and [111]. This behavior is interpreted in terms of the geometrical characteristics of the Fermi surface.

Pulsed laser irradiation of lead-implanted single-crystal copper films

We have studied the effect of pulsed laser annealing on single-crystal copper films implanted with lead to a concentration far in excess of equilibrium solid solubility. A Nd:YAG frequency-doubled 50-ns-pulsed laser was used, with power density up to 2.4 J/cm2. Channeling of 2-MeV helium ions was used to determine the concentration profile and degree of substitutionality of the lead both before and after laser irradiation. The near-surface region is melted if irradiated with a laser pulse of adequate energy density. The Pb atoms are redistributed and some accumulate near the sample surface. The fraction of Pb atoms which remain substitutional is nearly the same for as-implanted and laser-irradiated samples. This indicates that the rapid quenching following laser annealing (∼1011 K/sec) is almost as effective in retaining Pb atoms in metastable solution in Cu as the original effective quenching (∼1014 K/sec) following Pb implantation. Furnace annealing at 250 °C for 30 min greatly reduces the substitutional fraction of Pb atoms, as expected.

Epitaxy in the aqueous oxidation of (001) single crystal copper films

Observations are reported on the aqueous oxidation of copper single crystal films. A third copper/cuprous oxide epitaxial relationship has been found, which is related to the two epitaxial relationships already reported in the literature.

The structure of epitaxial overgrowths of Cu 2S formed on (111) Cu

Overgrowths of Cu 2S were formed on (111) single-crystal films of copper by exposing them to sulfur vapor in the temperature range 25–300 °C. Reflection high energy electron diffraction (RHEED) analysis revealed that the resultant overgrowths were epitaxial and of various structural forms depending predominantly on the duration of exposure and not on the temperature. The overgrowth started as a cubic form of Cu 2S but transformed to the hexagonal form and finally to the orthorhombic form. The morphology of the Cu 2S indicated by RHEED, scanning electron microscopy and transmission electron microscopy proceeds from a smooth flat structure to an island-type formation.

A new technique for preparation of thin single crystal films of copper

A new technique has been developed for the preparation of continuous thin single crystal films of copper of 180–250 å thick. The technique employs two stages of evaporation. During the first stage of evaporation copper nuclei approximately 800 Å thick are formed on a preheated mica substrate. These nuclei are then used to influence the lateral growth of subsequently deposited copper layers and thus to enhance the formation of a continuous single crystal film during the second stage of evaporation.

Oxide removal and desorption of oxygen from partly oxidized thin films of copper at low pressures

Partly oxidized copper films were annealed in a controlled vacuum of 10−7 Pa at a temperature of 450° C. The changes discussed below were observed in situ with a specially designed high-resolution transmission electron microscope. The thin, (100)-oriented, single-crystal films of copper had been oxidized immediately prior to the annealing studies at the same temperature and at an oxygen partial pressure of 7×10 −1 Pa, until the desired fraction of the copper film was converted to oxide. It was observed that the oxide disappeared during annealing as long as some copper was left unoxidized. The disappearance of the oxide is explained as being due to dissociation of the oxide at the oxide-metal interface followed by diffusion of oxygen into the metal and desorption of oxygen from the surface of the unoxidized copper. The rate of disappearance of the oxide was found to be proportional to the surface area of unoxidized copper, i.e., the desorption was found to be the rate — limiting step. In the case of heavily oxidized films (>50%), holes were observed to develop in the oxide near the oxide-metal interface after an annealing period of 2–3 hr. Upon resumption of the oxidation, these holes first disappeared, and the normal oxidation behavior was then resumed. The formation of holes may be explained by vacancy clustering. When completely oxidized films were annealed, recrystallization of the oxide was observed.

The resistivity of single-crystal copper films

The resistivity of single-crystal copper films

Optical transmittance and microgravimetric studies of the oxidation of 〈100〉 single crystal films of copper

Thin single crystal copper films have been grown and oxidized on (100) faces of cleaved sodium chloride discs suspended from a vacuum ultramicrobalance. Optical transmittance measurements between 400–800 nm and electron microscopic investigations were also used to characterize the oxidation process. Polycrystalline copper films grown at room temperature are substantially the same as those grown previously on glass substrates. Single crystalline growth at 325 ° C on rock salt produces a characteristic transmittance curve due to the “island” nature of the films. These curves compare favorably with other previously published results. Single crystal copper films oxidized to CuO0.67 at temperatures of 117–159°C in 100 Torr of oxygen for films less than 500 A thick. For films 378 to 1000 Å thick, compositions of CuO0.52 to CuO0.62 were obtained between 123–176°C. The oxidation to less than CuO0.67 is attributed to the existence of islands in these films which are thicker than the average film thickness, and require higher temperatures or thinner films to permit oxidation to CuO0.67 before the nucleation of CuO sets in.

Thermoelectric Voltage and Resistivity of Metallic Single-Crystal Films Epitaxially Grown by Vacuum Deposition

Single-crystal films of copper and (60Cu–40Ni) alloy were epitaxially grown on cleaved (001) surface of mica by vacuum deposition. Resistivity was measured for films with different crystal orientations prepared under various evaporating conditions, that is, operating pressure, substrate temperature, deposition rate and so on. The results obtained were as follows; (1) Epitaxially grown single-crystal films of copper with (111) orientation showed low resistivity compared with that of polycrystalline films, and size-effect anisotropy was observed when resistivities of films with <110> and <112> orientations were compared. (2) Thermoelectric voltage of Cu–(60Cu–40Ni) single-crystal film thermocouple was found to depend on crystal structures and crystal orientations of films.

A transmission electron microscope study of electrodeposited nickel films on (001) copper substrates

Nickel was electrodeposited on to (001) single-crystal copper films. Deposit thickness were in the range 10 Å to 500 Å. Bicrystals and stripped deposits were examined by transmission electron microscopy and high-resolution electron diffraction. Misfit, as a function of thickness, was determined from moiré fringe spacings, splitting of diffraction spots and the spacing of misfit dislocations. The misfit was found to be less than that of vapour-deposited films at corresponding thicknesses. The misfit as calculated from the spacing of misfit dislocations was not in agreement with the misfit as determined from moiré fringes or electron diffraction. These discrepancies might be due to foreign material incorporated in the deposit.

The oxidation of (100) single-crystal films of copper on (100) NaCl

Electron diffraction, electron microscopy, optical transmittance and microgravimetric techniques have been combined to study the oxidation of (100) single-crystal films of copper grown on (100) sodium chloride substrates at 325°C. The single-crystal films contained the usual “void” areas. Films 500 Å thick or less can be oxidized to CuO 0.67 readily at temperatures of 120°–180°C in 100 torr of oxygen. The oxide shows marked orientation but is not a single crystal. Oxidation to CuO yields polycrystalline oxide. A mechanism for forming CuO 0.67 from copper that is consistent with all the data involves an initial oxidation in which the “voids” are filled with oxide. The controlling rate then shifts to oxidation from the top of the grains towards the substrate interface until the copper is completely oxidized to CuO 0.67.

941. Obtaining epitaxial single crystal copper films with thickness of 5000 to 8000 Å and making more precise their orientation with the aid of the channelling effects: A M Markus and A L Faynshteyn, Ukr Fiz Zh, 15 (10), 1970, 1738–1740 ( in Russian)

941. Obtaining epitaxial single crystal copper films with thickness of 5000 to 8000 Å and making more precise their orientation with the aid of the channelling effects: A M Markus and A L Faynshteyn, Ukr Fiz Zh, 15 (10), 1970, 1738–1740 ( in Russian)

Ion-etch characteristics of epitaxial copper on sapphire

For the first time a face-centred-cubic metal film has been epitaxially grown on sapphire. Film crystallinity and ion-etch characteristics were studied using back reflection X-ray diffraction and scanning electron microscope techniques. Single-crystal copper films have been deposited on basal plane sapphire substrates in the temperature range 240 to 375° C. The films exhibited bulk metal resistivity. Ion-etching studies of the films, using argon ions, have demonstrated superior quality, resolution and vertical etch profile of interconnection transmission lines over those of polycrystalline or less crystalline films.

Role of deformation twins in the fracture of single-crystal films

Single-crystal films of copper, silver, gold, palladium, platinum and nickel were prepared by evaporation and were deformed by applying tensile stresses along the 〈110〉 and 〈100〉 directions in the (001) film plane. Deformation was accompanied by the generation of lenticular twins whose growth seemed to take place by the migration of twinning dislocations. The resolved shear stress on the {111} 〈11̄0〉 slip systems inside the deformation twins was larger than that on the twinning systems themselves. The formation of the twins was therefore followed by plastic deformation within the twins. This led to local thinning in the twins and finally to the formation of cracks.